1. Field of the Invention
The present invention relates to an ink jet printer head and an ink jet printer having the ink jet printer head.
2. Description of the Related Art
There is an actuator of a head equipped in an ink jet printer, which expands and restores the capacity of many ink storing chambers formed inside the actuator using a piezoelectric element installed corresponding to each of the ink storing chambers, and which applies pressure to the ink inside the ink storing chamber. In this way, the actuator discharges the ink from an ink discharge hole formed in each of the ink storing chambers to the external i.e., onto the recording sheet.
As one example of such an actuator, this is an actuator provided with: a base plate; a piezoelectric element member fixed on the base plate; a cavity plate, which is fixed on the piezoelectric element member and in which the ink storing chambers and ink flow paths to supply the ink to the ink storing chambers are formed.
The cavity plate is made from polyethersulfon etc., while the base plate is made from alumina etc., so that a displacement due to the piezoelectric effect by the piezoelectric element is efficiently reflected to the ink discharge.
However, in an ink jet printer of a so-called hot-melt type, in which a solid ink is heated and melted to be discharged, the temperature of the actuator portion becomes equal to or higher than about 120xc2x0 C. Thus, since the difference in the thermal expansion coefficient between the cavity plate and the piezoelectric element is relatively large, a positional shift or drift is generated between the position of the ink storing chamber and the piezoelectric element, resulting in that it is difficult to perform an efficient ink discharge, which is a problem.
Further, in the above mentioned actuator, 128 ink discharge holes are formed, for example, and the same number of the ink storing chambers and the piezoelectric elements respectively are prepared.
In such a construction, in case of expanding the ink storing chambers by actuating just one or a small number of the piezoelectric elements, the cavity plate made from the aforementioned material exhibits an enough rigidity or stiffness. However, in case of expanding all or a large number of the ink storing chambers by actuating all or a large number of the 128 piezoelectric elements, the rigidity of the cavity plate is not enough and the cavity plate is deformed. This result in that the difference between the capacities of the respective ink storing chambers are generated, so that it is not possible to perform a uniform ink discharge, which is another problem.
Given these circumstances, it is an object of the present invention to provide: an ink jet printer head of hot-melt type, which can perform an efficient ink discharge even if it is heated up to a relatively high temperature, and which can perform a uniform ink discharge even if a large number of piezoelectric elements thereof are simultaneously actuated; and an ink jet printer having such an ink jet printer head.
The above object of the present invention can be achieved by an ink jet printer head of hot-melt type for heating and melting solid ink and then discharging the melted ink onto a recording medium. The ink jet printer head is provided with: a cavity plate prescribing (i) an ink flow path through which the melted ink is supplied, (ii) a plurality of ink storing chambers, each of which is connected to the ink flow path in which the supplied ink is temporarily stored, and (iii) a plurality of ink discharge holes which are connected to respective one of the ink storing chambers though which the temporarily stored ink is discharged; a piezoelectric element member, which is opposed to the cavity plate and has a plurality of piezoelectric elements for selectively changing capacities of the ink storing chambers; and a base member for supporting the piezoelectric element member. The piezoelectric element member is interposed and fixed between the cavity plate and the base member. The cavity plate, the piezoelectric element member and the base member have thermal expansion coefficients equal or approximate to each other.
According to the ink jet printer head of the present invention, when the peripheral circumference of the ink flow path is heated-up in order to heat and melt the solid ink, the base member, the piezoelectric element member and the cavity plate are also heated-up, so that each of these constitutional elements are thermally expanded. At this time, since these constitutional elements have the thermal expansion coefficients equal or approximate to each other, these constitutional elements are thermally expanded in degrees same or similar to each other. This results in that the positional shift or drift between the position of the piezoelectric element and the position of the ink storing chamber corresponding to each other can be restrained depending on the degree of the approximation.
In one aspect of the ink jet printer head of the present invention, the cavity plate and the base member are made from ceramic, and elastic coefficients and thicknesses of the cavity plate and the base member are set so that a flexure amount thereof in a direction of discharging the ink be smaller than that of the piezoelectric element member.
According to this aspect, in case that the capacity of the ink storing chamber is changed by the piezoelectric effect of the piezoelectric element and that the internal pressure within the ink storing chamber is increased, the deformation of the cavity plate can be restrained, so that the variation in the capacities between the ink storing chambers are not practically generated. Further, although the force of the piezoelectric element applied to change the form of the cavity plate is also applied to the side of the base member, since the predetermined elastic coefficient and thickness are set for the base plate, this force of the piezoelectric element can be applied as a force applied to the side of the cavity plate. Thus, it is possible to change the capacity of the ink storing chamber enough to appropriately discharge the stored ink.
In another aspect of the ink jet printer head of the present invention, the ink jet printer head is further provided with a partition plate interposed and fixed between the cavity plate and the piezoelectric element member. The partition plate has a thermal expansion coefficient equal or approximate to that of respective one of the cavity plate, the piezoelectric element member and the base member.
According to this aspect, the displacement of the piezoelectric element is transmitted through the partition plate to the ink storing chamber. At this time, since the partition plate has the thermal expansion coefficient equal or approximate to that of respective one of the cavity plate, the piezoelectric element member and the base member, even if the peripheral circumference of the ink flow path including these constitutional elements is heated up, the displacement of the partition plate is still appropriate, so that the displacement of the piezoelectric element can be transmitted surely to the ink storing chamber.
In this aspect, the partition plate may comprise a diaphragm having elasticity. Thus, the ink storing chamber, which shape is once change by the displacement of the piezoelectric element, can be restored by the elasticity of the diaphragm.
In another aspect of the ink jet printer head of the present invention, the ink jet printer head is further provided with a nozzle plate, which is disposed on a surface of the cavity plate on a side of discharging the ink and in which a plurality of nozzle holes connected to respective one of the ink discharge holes are formed. The nozzle plate has a thermal expansion coefficient equal or approximate to that of respective one of the cavity plate, the piezoelectric element member and the base member.
According to this aspect, when the peripheral circumference of the ink flow path is heated up, the nozzle plate is also heated-up, and the force due to the increase of the internal pressure of the ink storing chamber is also applied to the nozzle plate. However, since the nozzle plate has a thermal expansion coefficient equal or approximate to that of respective one of the cavity plate, the piezoelectric element member and the base member, the degree of the expansion due to the applied heat and the deformation due to the application of the aforementioned force can be appropriately restrained. Thus, it is possible to appropriately discharge the ink.
In another aspect of the ink jet printer head of the present invention, the cavity plate and the base comprise same material.
According to this aspect, the thermal expansion coefficient as well as the elastic coefficient can be made same to each other between the cavity plate and the base member since they comprise the same material.
In this aspect, the same material may be alumina. In this case, cavity plate and the base plate can function appropriately to discharge the ink even if they are in the high temperature condition.
In another aspect of the ink jet printer head of the present invention, the piezoelectric element member comprises lead zirconate titanate.
According to this aspect, the thermal expansion coefficient as well as the elastic coefficient of the piezoelectric element member are appropriate to discharge the ink by the displacement of the piezoelectric element member.
The above object of the present invention can be also achieved by an ink jet printer provided with the above described ink jet printer head of the present invention or any one of the above described various aspects thereof, and a moving device for relatively moving the ink jet printer head with respect to the recording medium.
According to the ink jet printer of the present invention, since it is provided with the above described ink jet printer head of the present invention, the constitutional elements of the ink jet printer head are thermally expanded in degrees same or similar to each other. This results in that the positional shift or drift between the position of the piezoelectric element and the position of the ink storing chamber corresponding to each other in the ink jet printer head can be restrained depending on the degree of the approximation, so that it is possible to improve a printing quality.
The nature, utility, and further features of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiments of the invention when read in conjunction with the accompanying drawings briefly described below.